Purification of noble metal-metal oxide composite



United States Patent PURIFICATION OF NOBLE METAL-METAL OXIDE COMPOSITEHerbert R. Appell, North Riverside, Ill., assignor to Universal OilProducts Company, Des Plaines, Ill., a corporation of Delaware NoDrawing. Application April 30, 1953, Serial No. 352,308

19 Claims. (Cl. 252413) This application is a continuation-in-part of mycopending application Serial No. 149,646, filed March 14, 1950, nowabandoned.

This invention relates to the purification of noble metals and moreparticularly to a novel method of removing impurities from a compositeof a noble metal and a metal oxide.

Noble metals find particular utility for use as catalysts for conversionreactions and the noble metals either are contaminated with impuritiesduring the manufacturing and handling procedures or become contaminatedwith impurities during the conversion process. When utilized ascatalysts, the noble metals may be used as such but usually are incombination or association with a carrier material which generally is arefractory metal oxide.

.Such catalyst may find utility for effecting reactions of organiccompounds including dehydrogenation, hydrogenation, cyclization,hydrocracking, reforming, oxidation, etc. of organic compounds andparticularly of hydrocarbons. In some cases, the catalyst as preparedcontains undesirable impurities and the novel features of the presentinvention may be utilized to purify the catalyst or, in other cases, thecatalyst becomes contaminated with impurities during use in theconversion process. While the activity of the catalyst may be restoredpartly by oxidation to burn oif carbonaceous deposits therefrom, in mostinstances the activity of the catalyst is not restored to the desireddegree and the features of the present invention may be utilized toobtain the desired reactivation. In any event, it eventually isnecessary to replace the catalyst and the present invention offers anovel method of reactivating the catalyst.

In one embodiment the present invention relates to a method of purifyinga composite of a noble metal and a metal oxide and containing impuritieswhich comprises treating said composite with a concentrated acid anddissolving said impurities in the acid.

In another embodiment the present invention relates to a method ofpurifying a noble metal associated with an oxide of a metal in theleft-hand columns of groups III and IV of the periodic table whichcomprises treating said catalyst with a concentrated acid and dissolvingimpurities in the acid.

In a further embodiment the present invention relates to a method ofpurifying a composite of a noble metal and a metal oxide and containingmetal impurities which comprises treating said composite with aconcentrated acid to dissolve said impurities in the acid withoutsubstantial dissolving of the noble metal and metal oxide, and washingand calcining the thus treated composite.

In a specific embodiment the present invention relates to a method ofreactivating a platinum-alumina catalyst containing metal impuritieswhich comprises treating said catalyst with concentrated hydrochloricacid and dissolving metal impurities therein, separating purifiedcatalyst from impurities, and calcining said purified catalyst at atemperature of from about 700 F. to about 1100 F.

In a still further specific embodiment the present invention relates toa method of reactivating a catalyst comprising a noble metal and a metaloxide containing impurities which comprises treating said catalyst in afree oxygen-containing atmosphere at a temperature of from about 300 F.to about 1100 F., subsequently treating said catalyst with aconcentrated acid to dissolve said impurities in the acid withoutsubstantially dissolving the 2,704,281 Patented Mar. 15, 1955 ice noblemetal and metal oxide, and washing and calcining the thus treatedcomposite.

The noble metals for treatment in accordance with the present inventioninclude platinum, palladium, gold, silver, iridium, rhodium, ruthenium,oxmium, etc. As hereinbefore set forth, these noble metals, when used ascatalysts, are generally associated with a refractory metal oxide andparticularly an oxide of a metal in the left-hand columns of groups IIIand IV of the periodic table including particularly the oxides ofaluminum, titanium, zirconium, hafnium, thorium, etc. In some cases twoor more metal oxides may be included in the catalyst, and in othercases, activating components may be included in the catalyst. Theseactivating components generally are acidic and include halogens,particularly chlorine and fluorine, other mineral acids, organic acids,etc., the acidic component or components probably being associated withthe metal oxide and/ or metal in the combined state.

As hereinbefore set forth, the novel features of the present inventionmay be utilized for the purification of noble metals in association withrefractory metal oxides and also containing, when desired, an activatingcomponent, however, the novel features of the present invention areparticularly adapted to the reactivation of alumina-platinum-combinedhalogen catalyst which recently have been found to be of particularadvantage for use in the reforming of gasoline. In the interest ofsimplicity the following description will be directed to thereactivation of catalyst of this type with the understanding that thenovel features of the invention may similarly be applied to other noblemetals and other catalyst compositions.

When treating a noble metal in association with a refractory metaloxide, it is generally desired to remove undesirable impurities Withoutsubstantial removal or dissolving of the noble metal and refractorymetal oxide. In the past, it has been the practice to use dilute acidsin order not to dissolve the metal oxide. I have now found that,contrary to expectations, concentrated acids may be used satisfactorilyto obtain removal of impurities without substantial dissolving of thenoble metal or refractory metal oxide.

Any suitable concentrated acid may be used in accordance with thepresent invention, with the mineral acids being preferred, includinghydrochloric acid, hydrobromic acid, hydrofluoric acid, hydriodic acid,sulfuric acid, phosphoric acid, nitric acid, as well as some organicacids such as oxalic acid, formic acid, etc. Preferred acid compriseshydrochloric acid which generally will be in a concentration of aboveabout 35%, the commercially available hydrochloric acid being of theorder of 37% concentration and is satisfactory for use in accordancewith the present invention.

It has been found that improved results are obtained when theconcentrated acid is saturated with a metal salt corresponding to thatacid. For example, when hydrochloric acid is utilized for the treatmentof aluminanoble metal catalyst, aluminum chloride is dissolved thereinto the point of saturation. The amount of aluminum chloride Will ingeneral be very low and Will depend upon the concentration of the acidemployed. Similarly, when concentrated nitric acid is employed, itpreferably is saturated with aluminum nitrate or, When concentratedsulfuric acid is employed, it preferably is saturated with aluminumsulfate.

In accordance with the invention the catalyst, usually after use in thereforming process and containing metallic impurities, is treated asfollows: In one embodiment the catalyst may be subjected to an oxidationor burning operation to remove carbonaceous deposits therefrom or whendesired, this burning operation may be effected after the acidtreatment. When the carbon content of the catalyst is high it frequentlyis desirable to effect the burning or oxidizing of the catalyst prior tothe acid treatment in order that the acid may more easily penetrate intothe catalyst particles. When the catalyst is contacted with afree-oxygen-containing gas to effect oxidation of the carbon on thecatalyst to remove the same, care must be taken since most noble metalsare very active catalysts to effect the reaction between carbon andoxygen, and since the reaction is highly exothermic it is possible toobtain temperatures higher than are desired due to the high exothermicreaction.

The catalyst may be in any suitable particle size and usually will be inpreformed shapes of uniform size as produced by pelleting, extrusion orother suitable methods and these particles may be treated in accordancewith the present invention. Catalyst in the form of spheres may also bepurified by this method. When deslred, the catalyst may be ground intoparticles of irregular me and shape prior to either the oxidationtreatment or the and treatment.

Any free oxygen-containing gas may be used to effect the burning oroxidation of the catalyst and air has been found to be satisfactory touse for the reactivation. In one method a low free oxygen-containing gasmay be passed over the catalyst at substantially room temperature andthe temperature in the reaction zone may be slowly increased while atthe same time increasing the percent of free oxygen until the desiredreactivation temperature is obtained and essentially pure air 1s usedfor the reactivation. The burning or oxidation treatment is usuallyconducted in a temperature range of from about 300 F. to about 1100 F.The time of contact is inversely proportional to the temperatureemployed, that is, with higher temperatures shorter times are employed,however, in general the burning or oxidation will be effected for atleast 15 minutes and time in excess of 12 hours are not particularlybeneficial, especially at the higher temperatures.

The acid treatment may be effected in any suitable manner, which may beeither a batch type of operation or a continuous type of operation. In abatch type of operation, the pills may be disposed in a zone and theacid poured over the pills or a zone may be partly filled with the acidand the catalyst then introduced thereto. In general, it is preferred touse an excess of cold acid because the reaction is exothermic and theexcess cold acid will tend to absorb the heat of reaction. In anotherembodiment the catalyst may be permitted to absorb moisture from theatmosphere or by any other suitable means before the acid treatment asthis further serves to reduce the exothermic heat of absorption. Ingeneral, the treatment should be effected at a temperature not greaterthan about 150 F. and preferably of the order of about 30 to about 90 F.The optimum temperature is dependent upon the acid, usually lowertemperatures are more suitable for the stronger acids. In asemi-continuous type of operation the catalyst may be disposed in aconfined zone and the acid passed therethrough in either upward ordownward flow. In a continuous type of operation the catalyst and acidmay be passed through a treating zone, either in countercurrent orconcurrent flow to each other and each being continuously withdrawn fromthe treating zone, the catalyst separated by filtration or othersuitable means from acid, and the acid being recycled for further usewithin the process, either with or without separation of the impurities.Preferably, however, it will be necessary to separate the impuritiesfrom the acid prior to recycling thereof and this may be accomplished inany suitable manner, such as by distillation, solvent extraction, etc.In some cases, it may be desirable to effect the treatment in two ormore successive steps.

The time of treatment will depend upon the impurities in the catalystbut, in general, will vary from about 1 minute to 2 hours or more. Thistreatment will remove metallic impurities such as those of iron, nickel,sodium, etc. The necessary time of treatment may be determined byanalyzing the acid withdrawn from the treating zone to determine itsiron or other metallic content. The treatment will be continued untilthe acid is substantially free from iron or other impurities, thusestablishing the effect of the treatment to remove impurities from thecatalyst. For example, the acid when treating a catalyst as hereinbeforedescribed was originally colorless and during operation turned to a palegreen color to show the presence of iron. The operation was continueduntil the acid again became colorless and, therefore, did not containiron impurities.

After the catalyst has been treated with acid, it may be washed toremove chlorine or other soluble impurities and this treatmentpreferably is effected at a temperature of below about 200 F. andusually, for convenience, at normal or room temperature. When treating acatalyst containing a halide, and particularly a chloride, in

an amount in excess of that desired, the catalyst may be treated by ionexchange with a suitable reagent, such as ammonium nitrate or the like,to remove the excess halides and particularly chlorides. The catalystthen is usually washed and is dried at a temperature of from about 200F. to about 600 F. for 2 to about 24 hours or more and finally calcined,preferably in air, at a temperature of from about 700 F. to about 1100F. for about 1 hour to about 12 hours or more. When desired, thecatalyst may be gradually heated to drying temperature and maintained atthat temperature for the desired time and then is heated to the highertemperature desired for calcination and held at that temperature for thede sired time. The calcination treatment in air serves to burn offcarbonaceous deposits when not previously removed as hereinbefore setforth.

When the catalyst to be treated in accordance with the present inventionis in the form of particles of definite sizes and shapes andparticularly pills or pellets of uniform size and shape as may be formedby pelleting, extrusion or other suitable methods, it is preferred thatthe treatment will not weaken the strength of the catalyst particles. Ithas been found that treatment with concentrated hydrochloric acid orconcentrated nitric acid does not substantially weaken the structuralstrength of the catalyst pills, especially when the catalyst issubjected to calcination in air subsequent to the acid treatment.

The following examples are introduced to illustrate further the noveltyand utility of the present invention but not with the intention ofunduly limiting the same.

Example I The catalyst used in the following examples comprised alumina,0.3% by weight of platinum, 0.12% by weight of combined fluorine and0.45% by weight of combined chlorine and was in the form of Ms x Mapills. This catalyst had been used for the reforming of a Midcontinentnaphtha for a period of 139 days in a pilot plant operation. In order tocompare on an equal basis the activity of the catalyst after the varioustreatments, dif ferent samples of the catalyst, as received from thepilot plant and after various treatments to be hereinafter set forth,were utilized for the reforming of a Midcontinent naphtha in a test unitoperating at a temperature of 977 F., a pressure of 300 pounds persquare inch and utilizing a hydrogenzhydrocarbon mol ratio of 1.8:1.This test was continued for a period of 18 hours.

When tested in this manner, the catalyst as received from the pilotplant produced a gasoline product having an initial specific dispersionof 136.2 but after 18 hours of operation the specific dispersion of thegasoline product dropped to 115.8. The specific dispersion of thegasoline product is an indication of the aromatic content of thegasoline. A higher specific dispersion indicates a hlgher aromaticcontent and conversely a lower specific dispersion indicates a loweraromatic content.

In order to determine whether the deactivation of the catalyst was dueto the deposition of carbonaceous material thereon, a sample of thecatalyst was subjected to oxidation in the presence of air at atemperature gradually lncreasing to 925 F. and maintained at thattemperaturefor 1 hour. The regenerated catalyst was tested as describedabove and the initial specific dispersion of the gasoline product was140.3 which after 18 hours fell to 125.6. This, therefore, shows thatburning of the carbonaceous deposits from the catalyst, while restoringthe mitlal activity of the catalyst, did not restore the life of thecatalyst because the specific dispersion of the product fell to 125.6.

Therefore, it is concluded that the cause of deactivatron of thecatalyst is due to other reasons and more particularly to metallicimpurities in the catalyst. However, in an attempt to measure themetallic impurities in the catalyst by emission analysis, it was foundthat these results were not conclusive apparently due to the smallamounts of metals in the catalyst. However, when treat mg the catalystwith concentrated acid, the effluent acid gave a strong test for iron.This definitely proves the presence of metallic impurities, and thebelief that these impurities deactivate the catalyst is confirmed by theimproved results obtained with the acid treated catalyst.

Another sample of the spent catalyst from the pilot plant was treatedwith concentrated hydrochloric acid saturated with aluminum chloride asfollows. 15 grams of aluminum chloride hexahydrate were added to 500 ml.

of 37% concentration hydrochloric acid and the mixture was allowed tostand overnight. 100 ml. of this solution was placed in a flask and 42.9guts. of catalyst received from the pilot plant were gradually addedthereto. The solution became quite warm and gradually turned a palegreen. The solution was withdrawn from the catalyst and when tested withthiocyanate reagent gave a strong test for iron. The catalyst wasextracted three more times with additional concentrated hydrochloricacid solution saturated with aluminum chloride, and the last efiiuentacid gave a negative test for iron. The catalyst pills were in contactwith the acid for a total of 2 hours. The catalyst pills were thenrinsed and washed thoroughly with water, after which the catalyst pillswere treated with 5% ammonium nitrate solution to remove excesschlorine, and were again washed with water. The pills were then oxidizedat a temperature gradually increasing to 932 F. and maintained at thattemperature for 1 hour in order to burn off carbonaceous depositstherefrom.

When tested in the manner hereinbefore set forth, the acid treated andcalcined catalyst pills produced a gasoline product having an initialspecific dispersion of 139.5 and a final specific dispersion after 18hours of 136.6. It is seen from these data that the initial activity ofthe catalyst was substantially restored and that the life of thecatalyst was greatly improved because the specific dispersion dropped toonly 136.6 after 18 hours as compared to a drop to 115.8 for theuntreated catalyst and to a drop to 125.6 for the catalyst which hadbeen regenerated only by burning carbonaceous deposits therefrom.Further, the structural strength of the catalyst pills was not impairedby this treatment.

Example II A sample of an alumina-platinum catalyst was treated withconcentrated nitric acid saturated with aluminum nitrate. This treatmentremoved metallic impurities from the catalyst but did not dissolve thealumina or platinum to any noticeable extent.

Example III A zirconia catalyst was treated with concentratedhydrochloric acid saturated with aluminum chloride and it was found thatthe zirconia did not dissolve in the concentrated acid.

Example IV A titanium oxide catalyst was treated with concentratedhydrochloric acid saturated with aluminum chloride and here again it wasfound that the titanium oxide was not dissolved to a noticeable extent.

I claim as my invention:

1. A method of purifying a composite of a noble metal and a metal oxideand containing metal impurities which comprises treating said compositewith a concentrated acid to dissolve said impurities in the acid withoutsubstantial dissolving of the noble metal and metal oxide, and washingand calcining the thus treated composite.

2. A method of purifying a composite of a noble metal and a metal oxideand containing metal impurities which comprises treating said compositewith a concentrated mineral acid saturated with a metal salt of saidacid to dissolve said impurities in the acid without substantialdissolving of the noble metal and metal oxide, and washing and calciningthe thus treated composite.

3. A method of purifying a composite of a noble metal and a metal oxideand containing metal impurities which comprises treating said compositewith concentrated hydrochloric acid to dissolve said impurities in theacid without substantial dissolving of the noble metal and metal oxide,and washing and calcining the thus treated composite.

4. A method of purifying a composite of a noble metal and alumina andcontaining metal impurities which com-.v

prises treating said composite with concentrated hydrochloric acidsaturated with aluminum chloride to dissolve said impurities in the acidwithout substantial dissolving of the noble metal and metal oxide, andwashing and calcining the thus treated composite.

5. A method of purifying a composite of platinum and a metal oxide andcontaining metal impurities which comprises treating said composite withconcentrated hydrochloric acid to dissolve said impurities in the acidwithout substantial dissolving of the noble metal and metal oxide, andwashing and calcining the thus treated composite.

6. A method of purifying a catalyst composite comprising a noble metaland a metal oxide and containing metal impurities which comprisestreating said composite with a concentrated mineral acid to dissolvesaid metal impurities in the acid without substantial dissolving of thenoble metal and metal oxide, and washing and calcining the thus treatedcomposite.

7. A method of purifying a catalyst comprising a noble metal and anoxide of a metal in the left-hand columns of groups III and IV of theperiodic table and containing metal impurities, which comprises treatingsaid catalyst with a concentrated mineral acid to dissolve said metalimpurities in the acid without substantially dissolving the noble metaland metal oxide withdrawing said acid, and subjecting said catalyst tocalcination at a temperature of from about 700 to about 1100 F.

8. The method of claim 7 further characterized in that said oxidecomprises aluminum oxide.

9. The method of claim 7 further characterized in that said oxidecomprises zirconium oxide.

10. The method of claim 7 further characterized in that said oxidecomprises titanium oxide.

11. The method of claim 7 further characterized in that said oxidecomprises thorium oxide.

12. A method of reactivating an alumina-platinum catalyst containingmetal impurities which comprises treating said catalyst withconcentrated hydrochloric acid at a temperature below about F. wherebyto dissolve metal impurities in said acid, without substantiallydissolving the platinum and alumina, removing acid containing metalimpurities from the catalyst, and calcining said catalyst in thepresence of air at a temperature of from about 700 F. to about 1100 F.

13. The method of claim 12 further characterized in that saidconcentrated hydrochloric acid is saturated with aluminum chloride.

14. The method of claim 12 further characterized in that said catalystalso contains combined halogen.

15. A method of reactivating a catalyst comprising a noble metal and ametal oxide, containing metal impurities and carbon which comprisesheating said catalyst in a free oxygen-containing gas at a temperatureof from about 300 F. to about 1100 F., subsequently treating saidcatalyst with a concentrated acid to dissolve said impurities in theacid without substantially dissolving the noble metal and metal oxide.

16. A method of reactivating an alumina-platinum catalyst containingmetal impurities and carbon which comprises heating said catalyst in afree oxygen-containing atmosphere at a temperature of from about 300 F.to about 1100 F., subsequently treating said catalyst with concentratedhydrochloric acid at a temperature below about 150 F. whereby todissolve metal impurities in said acid without substantially dissolvingthe platinum and alumina, removing acid containing metal impurities fromthe catalyst and calcining said catalyst.

17. The method of claim 16 further characterized in that saidconcentrated hydrochloric acid is saturated with aluminum chloride.

18. The method of claim 16 further characterized in that said catalystalso contains combined fluorine.

19. The method of claim 16 further characterized in that said catalystalso contains combined chlorine.

References Cited in the file of this patent UNITED STATES PATENTS2,006,221 Ridler June 25, 1935 2,344,208 Kirkpatrick Mar. 14, 19442,346,844 Hull Apr. 18, 1944 2,456,633 Haensel Dec. 21, 1948 2,474,440Smith et a1. June 28, 1949

1. A METHOD OF PURIFYING A COMPOSITE OF A NOBLE METAL AND A METAL OXIDE AND CONTAINING METAL IMPURITIES WHICH COMPRISES TREATING SAID COMPOSITE WITH CONCENTRATED ACID TO DISSOLVE SAID IMPURITIES IN THE ACID WITHOUT SUBSTANTIAL DISSOLVING OF THE NOBLE METAL AND METAL OXIDE, AND WASHING AND CALCINING THE THUS TREATED COMPOSITE. 